Anthony Gregory has assembled a very useful resource on libertarianism and war that is well worth bookmarking. He links to the full spectrum of libertarian opinion on the subject, and devotes some time specifically to the Civil War and the world wars. He makes kind reference to my book with Murray Polner, We Who Dared to Say No to War: American Antiwar Writing from 1812 to Now. This presentation is my own most systematic discussion of the subject: